Optical fiber is fast becoming a transmission medium of choice for many communication networks because of the speed and bandwidth advantages associated with optical transmission. In addition, WDM is used to meet the increasing demands for more capacity in optical communication networks. As is well known, WDM combines many optical channels each at a different wavelength for simultaneous transmission as a composite optical signal in a single optical fiber.
Management of this increased capacity in WDM systems, e.g., managing the routing of communications traffic in many different optical channels on a wavelength-by-wavelength basis, is an important aspect of many WDM-based communication networks. For example, a desirable feature for many WDM networks is the capability to change routing of traffic among the different optical channels at certain nodes in the network to accommodate different users' requirements or changing requirements of a particular user. Certain types of network elements are deployed in WDM networks for such purposes. By way of example, cross-connects, add/drop multiplexers, optical switching arrangements, and the like are used at nodes in a WDM network to change the routing of individual optical channels (e.g., via cross-connections), to add or drop selected optical channels at particular nodes, and so on.
FIG. 1 shows one exemplary node 100 in a typical WDM network that is interconnected to many other nodes (not shown) by respective WDM optical line systems 101–104 via transmission paths 111–114. Although node 100 is shown in simplified form, it is assumed for this example that each of optical line systems 101–104 supports bi-directional communication via paths 111 114, wherein multiple optical fibers may be employed for such purpose. As such, it is also assumed that each of transmission paths 111–114 carries one or more WDM signals each having a number of optical channels.
In a so-called large node configuration, for example, node 100 might typically include a network element such as cross-connect 120 to switch or otherwise route traffic carried by individual optical channels of the WDM signals from one transmission path to another. For example, cross-connect 120 might be used to route communications traffic from an optical channel in the incoming WDM signal on path 111 to an optical channel in the outgoing WDM signal on path 114. Various cross-connect network elements employing either electronic, optical, or other switching fabrics are known to those skilled in the art. In general, these cross-connects are typically very costly and add a significant amount of complexity at a given node in the network. As such, cross-connects are generally reserved for use at the so-called larger network nodes. Add/drop multiplexers and other less costly and less complex network elements are typically found in the other network nodes that provide some limited routing functionality. However, these types of network elements are generally only used for managing a subset of the total number of optical channels that are being dropped and added in the WDM signal being processed at that node.
Accordingly, it would be desirable to provide a lower cost and more robust wavelength-selective routing capability at nodes in a WDM network that do not have a cross-connect network element or the like.